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Why do we need a negative derivative of the pitching moment? restoring moment should be enough?
I am wondering why I read everywhere, that for static stability (longitudinal) the slope of the lift coefficient has to be negative.
Imagine a curve (cm= coefficient of moment , alpha = angle of attack) like the one on my picture. In the trimmed condition where c_m=0 : when I have a an increase in angle of attack, it should be enough, when c_m is negative, because I will always have a restoring moment. The more negative it is, the stronger the restoring moment.
So also when the slope is increasing, I am still in the negative area like in the red area of the picture with a restoring moment.
What I can imagine: such a slope of cm over alpha for a whole aircraftwill maybe not exist?
Thank you for your comments and thoughts

So let’s assume the aircraft has a $C_{m_a}$ curve as you show. When you start to pull up you will feel nose down force on the yoke because of negative pitching moment. As you further increase the pull, the force required should increase also. However in your picture at some point the negative pitching moment $C_m$ decreases (in magnitude), still negative though. That can cause all unwanted motions in the aircraft because suddenly the force you are applying is becoming too excessive. It can even over-g the aircraft depending on the conditions. You are basically braking the linear response of the aircraft.
Ironically enough , that was the main reason Boeing 737 Max was equipped with MCAS in the first place. The stick force per g was not linear at some corners of the envelope. So they put MCAS to linearize the $C_{m_a}$, initially. Of course then they extend it to low speed region also.
Additionally, Part 25 Airworthiness Standards for big aircrafts requires stick force curve slope to have a stable slope:

§25.175   Demonstration of static longitudinal stability.
…
(1) With the landing gear retracted at high speed, the stick force curve must have a stable slope at all speeds within a range which is the greater of 15 percent of the trim speed plus the resulting free return speed range, or 50 knots plus the resulting free return speed range, above and below the trim speed (except that the speed range need not include speeds less than 1.3 $V_{SR1}$, nor speeds greater than $V_{FC}$ / $M_{FC}$, nor speeds that require a stick force of more than 50 pounds), with—

As for the small aircrafts the Part 23 requirement has a little bit of a leeway:

§23.2145   Stability.
(a) Airplanes not certified for aerobatics must—
…..
(3) Provide stable control force feedback throughout the operating envelope.

The part you are asking is specifically addressed in FAA AC25-7C:

§26
...
There may be no force reversal at any speed that can be obtained, except lower than the minimum for steady, unstalled flight or, higher than the landing gear or wing flap operating limit speed or VFC/MFC, whichever is appropriate for the test configuration.
...
(4) Examples of “local reversals” are given in Figure 26-2. Curves A and C depict a local gradient reversal within the required speed range. Even though it might be argued that the “average gradient” meets the one pound in six knots criterion, the gradient reversals would render these characteristics unacceptable. Curve B depicts a situation in which the gradient reverses, but only outside the required speed range. In addition, Curve B demonstrates a situation in which the local gradient does not always meet the required one pound in six knots, even though the average gradient does.

How do you get a "natural" stick force per G profile in the first place when the elevators are hydraulically powered with artificially generated feel?  Would it be better to say the airplane's response to the artificial stick force profile deviated from the other 737s, which was the only reason they incorporated it - to maintain the common type rating.

The way you expressed it sounds like the reason Boeing initially came up with MCAS was to differ extra the certification steps, because it was not flying like other 737s. However that’s not the case. They came up with MCAS because there was an aerodynamic problem with it. And that was the pitching up tendency of the aircraft at high speed wind up turns. So initially, it was a fix to an aerodynamic problem rather than a check off of certification requirements. This article mentions a little bit of the engineering background. Of course, later on things have changed.

@JohnK It's not the artificial feel that was the problem. It was purely aerodynamics (according to public knowledge thus far). You can have a passive column/sidestick and still have the same issue.

I was thinking in terms of stick displacement required per G vs force but it works out to be the same thing in the end with either artificial or natural feel.  Anyway, I understood that the pitch up characteristic described would have been acceptable from a cert standpoint had they designated the MAX as a new type from a pilot training perspective.  This happened on the CRJ1000.  Bombardier tried desperately to keep it in the same type rating family but Transport Canada just wouldn't go along, saying the differences added up to too much.

Remember that when you are analysing stability, you are interested in the derivatives by the parameter in question, not in the absolute magnitude. In longitudinal motion, you are mostly interested in how the balance changes when AoA changes. It is understood that in static motion, the absolute moment will be trimmed out (normally by tail) - otherwise it woudln't be static. Stability is usually analysed around a given static point.
On the picture, the derivative is the slope of the curve. Let's break it up in three parts.

When the curve is above the X axis ($c_m$ is positive, slope is negative), you have a stable situation with positive (pitch-up) moment. This moment will need to be compensated with an additional negative moment from the tail if we are to fly in this region statically. For a classic airplane, this is often a desirable situation because it reduces the trim drag. (But we need to consider the whole system to calculate if it's indeed more efficient).
When the curve is below X but still has negative slope, everything is the same except that the tail will need to provide an additional positive static moment, often at the cost of negative tail lift.
In the selected region with positive slope, you have an unstable derivative and pitch-up static moment. Is it that good? If you want to fly in this region, you'll trim out the absolute moment (effectively moving the curve up). Then, as you can see, still any increase in AoA will produce a positive (pitch-up) moment, driving it to further increase AoA.

If the curve represents the moment of a given fixed airplane configuration, the airplane will settle on the crossover point where $c_m = 0$, and we can see which AoA it will have. (By the way, given that $c_m$ is more or less independent of speed, this demonstrates that trim actually sets a fixed angle of attack rather than anything else).
But you are right in the sense that if, again, we consider the situation 'as is', i.e. trimmed and fixed as depicted, the aircraft will still 'slide back' to the stable trimmed point even from the shaded region, just less eagerly. However, if you continue the curve further, it will often cross $c_m = 0$ again, and past there will create a true runaway situation. In many aircraft, it will then bend down again and become stable, crossing the axis for the third time, now with a stable secondary trim point. This is typically a deep stall situation.

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Identify this USAAF biplane
I have been unable to match this USAAF biplane with a similar photo mainly due to the cockpit canopy. I've found no other like it.  I believe the photo was taken at Madison, WI or Chicago, IL in the 1930s.  Written on the photo was "Douglas Military Observation Plane." I am hoping to find out the make, model, version, and if possible the Military Unit.

That is a Douglas O-38E, with sliding cockpit windows and rounded tail.
The tail on the right of the picture is also a Douglas O-38, but another version (standard, B,C & F had such tails)

Source: wikimedia Photographer: USAF
It seems that the picture in the question is damaged; there are some stains covering the area below the horizontal tailplane and also the arms crest on the fuselage. It seems that the arms crest is a circle with a cross in it. This is the insignia of the 33rd division,  Illinois National Guard.
Some of their other O-38's are pictured here
A picture of possibly the same aircraft with the insignia clearly visible can be found on alamy.com

Dear DeltaLima, you nailed another one for me, and so quickly too.  Please know that I really try to identify these planes myself and not bother others for what I feel I should be able to do. But I get so frustrated when I spend an hour or two trying to identify a plane online with every description I can think of yet I come up empty-handed. Your knowledge of aircraft is exceptional. And yes, my photograph is damaged as you described.  I never would have figured out the insignia was a cross like in the photo you posted above. Once again, my sincere appreciation for all the help you have given.

@FreshBreeze you're very welcome. I enjoy doing a little search like this. The insignia was the most difficult part of this one. Before I realised the picture was damaged, I thought I was looking at an eagle! Question for you: your profile shows that you are in Pattaya. Are you there now? What is the situation there regarding covid?

Like you, I thought the insignia was an eagle also.  I knew it was damaged, but so closely resembled a bird that I assumed the same. Funny how some things can be very misleading.  Yes, I'm living in Pattaya, one of the few leftovers. It's been my home for 19 years. Last year we were locked down for at least 6 months. Then restrictions were eased up and we got through Christmas. But right at NYE some illegals from Myanmar brought some cases in and we were locked down again until Feb 1st. A few bars and restaurants are open, but it is a ghost town. Still heavy travel restrictions & no tourists.

@FreshBreeze I hope you can stick around and help  others with your knowledge too - if not here then perhaps on photography.se

@FreshBreeze thank you for the info. My wife spent most of here childhood in Pattaya and her parents still live there for most of the year. Like most foreigners, they have left during spring and are now basically unable to return. Pattaya without tourists and foreigners must be a strange experience and I imagine the economic consequences for many Thai people are terrible. We're planning to visit after things return to normal.

@DeltaLima I feel sorry for the millions of people who have been adversely affected economically, not only here, but throughout the world. Thais have suffered immensely. Thousands who worked in Pattaya had to return to their villages and parent's farm to survive. As for retired me, it hasn't been a huge change other than periods of being unable to meet with my friends. I'm married and raising a daughter so I'm pretty much a homebody anyway. When you are able to come and visit, I would enjoy meeting you personally. How can we contact other than here?

@Jamiec Thank you for your friendly encouragement to stick around.  I confess I will probably have more questions than I can contribute in answers, but I really am happy I found this website and look forward to continued interaction. The expertise of members here is overwhelming.  As per your suggestion, I'll also check out photography.se.

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Example of where Class Echo abuts class Golf
Aeronautical Chart Users' Guide shows an example of a fuzzy magenta line bordering with class Golf airspace. I tried to look but couldn't find any examples on the charts. If you have seen it, please point me in the right direction. Much appreciated!

There is an example in Alaska: the Cape Lisburne LRRS Airport.
As a bonus, note the rare NDB-DME and LF/MF airway (Blue 2)!

You also got the pretty uncommon sea lion protection area marker.


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FAA test question about load factor
The following question is from the FAA PAR (Private Pilot, Airplane) exam :

The load factor on an airplane increases with :
(A) Any moderate change in pitch attitude, increase in weight, and steep turns.
(B) Increase in weight, an increase in power, and any moderate pitch changes.
(C) Increase in weight, steep turns, and abrupt changes in airplane attitude.

The correct answer is supposed to be (C).
All of the answers say that load factor increases with an increase in weight. However, load factor is inversely proportional to weight by definition.
What am I misunderstanding?
Edit: I think it is supposed to say "load" instead of "load factor" but it was not written that way.

Weight is the force on a mass from acceleration. The aircraft mass is constant, so if the weight increases, it must be from an increase in acceleration. Load factor is the ratio between normal acceleration and gravitational acceleration, hence weight goes up with load factor. What surprises me is that the FAA does not confuse weight with mass, as they usually do in those exams.

@PeterKämpf The weight of an airplane does not change (appreciably) during flight maneuvers (e.g. steep turns). It is the force due to gravity, not the force due to acceleration. The load factor is 2g in a constant altitude 60 degree turn, so the pilot feels twice as heavy. However, his weight has not actually increased.

You are confusing weight with mass. What's your weight on the lunar surface?

No I’m not. I think you are confusing fictitious forces with weight. Are you saying that an airplane in a coordinated 60 degree constant-altitude turn literally becomes twice as heavy?

Yes, it has twice the weight and therefore needs twice the lift. Mass will stay constant, though. Which unit do you use for weight, and which for mass?

Please explain to me how the weight changes if the mass is constant and the distance from the earth is constant...

There are several definitions of weight. @PeterKämpf is referring to apparent weight. More common definitions of weight include the local gravitation, but exclude non-gravitational acceleration.

@bogl Thanks for helping. The point is that weight is a force and mass is mass. Using the same units for both in Imperial units clouds the distinction, as this question demonstrates. Since gravitational and inertial accelerations are indistinguishable in their effects, it does not make sense to narrowly define weight as only the part of the force caused by gravity. What would be the word for the other part? Weight maybe?

@PeterKämpf Unfortunately, the inability to distinguish mass and weight is not limited to countries with imperial units.

@PeterKämpf [apparent weight] - [ISO weight] = [innate force] + [buoyancy]

I agree that this can be confusing.
The load factor is indeed inversely proportional to weight, unlike the load factor on an aeroplane, which might be thought of as the lift required divided by the certified MTOW for the category of operation (g limit).  If the aircraft is in a steady 1 g flight at MTOW, the load factor to achieve this is one.  Start turning in a steep bank and the load factor becomes two in relation to the design load factor of the aeroplane's structure. If you then reduce the weight of the aircraft to, say, half the MTOW, the load factor in 1 g flight is a half of the load factor the aircraft was designed for.
The load factor on an aeroplane differs from the abstract concept of load factor as it relates to the load imposed on the aircraft compared to the load imposed on the aircraft when operating at gross weight at 1 g.
I hope this helps.

FAA exam questions are hopeless.  Also there are several different definitions of load factor.  The one that would appear to apply in this context ought to be invariant with weight, for any given G-loading.  It's basically the same thing as the G-loading.  Its the aerodynamic force divided by weight of aircraft plus contents.  1000 pound aircraft, generating 3000 pounds of force, has a load factor of 3.
On the other hand if we hold the aerodynamic force constant and we increase the weight then we decrease the G-load or load factor-- as the original question pointed out.


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Deployment of leading or trailing edge flaps - increase or decrease the angle of attack and critical angle of attack?
There are a number of similar questions, but I'd like to clarify the increase or decreases between the angle of attack and critical angle of attack. According to this article, "When the pilot lowers the flaps, two things immediately happen: the wing camber and the AOA both increase."
With regards to leading and trailing edge flaps is it accurate to say deployment will increase AoA and the critical AoA?

How does AOA change?
The angle of attack (AOA) is defined as as the angle between the chord line and the relative wind. When flaps and slats are deployed, the effective chord line changes. This is already nicely illustrated for trailing edge flaps in the article you linked:

(boldmethod.com)
As you can see, the new chord line has a higher angle compared to the relative wind, which results in an increase of AOA. Combined with the increase in camber, this will result in more lift (at the same airspeed), which means the pilot will usually reduce pitch to lower the AOA again when flaps are deployed.
I modified this image to illustrate the same for slats:

Now the new chord line is at a slightly lower angle compared to the relative wind, which results in a reduced AOA. The same is true for other leading edge devices (like e.g. Krueger flaps).
How does critical AOA change?
This depends on the exact type of device used. The following graphic shows how the coefficient of lift $C_L$ as a function of AOA $\alpha$ changes with various trailing edge high lift devices:

(HAW Hamburg - Aircraft Design)
For the slotted flap, critical AOA remains unchanged, but for all other types shown here critical AOA is reduced when deploying flaps. Note however that the maximum lift coefficient is always higher. The reason for the change in slope for extending flaps is already explained here: Why does lift curve slope increase when Fowler Flaps are deployed?.
The following graphic shows the same for leading edge high lift devices:

(HAW Hamburg - Aircraft Design)
Here, critical AOA is always increased compared to the clean wing.

Fantastic answer, thanks for your contribution.

the wing camber and AOA both increase

Let's look at the lift equation:
$Lift$ = Air density x wing area x Lift Coefficient x V$^2$
Lift Coefficient factor can be expressed as airfoil type (camber) at a given AOA.
When you lower flaps (for that portion of the wing) camber and AOA are indeed both increased but... the wing is producing more lift at that speed, which would encourage the pilot to lower AOA for the entire plane.  This is a good move to prevent tip stalls, but ...
Lowering flaps also increases drag, so more throttle is generally required to maintain airspeed.
Slats lower AOA when deployed but increase camber.  We can see that putting flaps near the fuselage and slats near the wing tips is a great safety combination.
Earlier aircraft (and many models) use "wing washout" for the same effect.  The benefits of retractable slats and flaps are that:  at higher cruise speeds "pulling them in" yields an improvement in fuel consumption efficiency from less drag.

increase AOA and critical AOA?

Better said that flaps will lower your stall speed (which you do not want to be near at low altitude) due to increase in camber.  For example, when aborting an approach to landing with flaps, avoid the temptation to yank the nose skyward to climb out.  Add power. At higher flaps settings, your stall angle relative to the horizon may be lower than with flaps up.
Significant increases in critical AOA can be had with leading edge slots, but again with significant drag penalty, requiring more power.


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Why don't the magnetic compass and direction indicator spin the same direction?
You set a direction indicator (DI) based on the magnetic compass in certain GA aircraft, e.g. Cessna 172. During training you're taught how to align the DI with the compass, the DI being the opposite side to the compass. Why haven't they been designed in a way to make them visually match to make it easier to set the DI?
This illustrates what I mean:
Compass
|||330|||
 ^

DI
|||330|||
       ^

I think I understand your question, and I know what you mean - it's something I have to sometimes think about when setting the DI.
However, I think your premise is slightly flawed. The issue isn't "compass vs DI", it's the difference between viewing a compass from the top down, vs head on.
If you look at a magnetic compass compass which can be used both ways (Such as this one you'll see that sideways on, it looks the same as the aircraft compass as in it increments right to left. But from the top, it's identical to any DI and increments clockwise - however, it reads "upside down" compared to a normal top-down map reading compass.
I'm not even sure if this would work, but I think what you're asking is for the DI to be upside down. This would go against most concepts that "up" is equal to forward.

Great explanation, makes sense.

+1 for reference to boat compass that can be viewed from above to read the card "on the back side".  The link is now broken, but in the past I mounted a compass like that one for cloud flying experiments in several aircraft (including a hang glider) because it was so much more intuitive to read in a confusing situation.

In ye olden tymes, as in the 1950s, DGs had a rotating drum presentation the same as the wet compass because the graduated drum was part of the gyro itself and rotated with it, like a compass does.  When I learned to fly in the 70s about half of the airplanes I'd encounter had an old drum DG.

The vertical card DG appeared in GA in the 60s, with a vertical card geared to move the opposite way, because they were easier to orient yourself with when flying, but in doing so the compass card necessarily moved the opposite way to the wet compass, which is just a magnet on a spike.
It takes a bit of mental effort to orient yourself, but really, when you set the DG you just have to be able to interpret the static position of the wet compass card and flip the progression of the numbers in your mind when figuring out what heading it shows.  It's not like you have to track a wet compass card's movement while in a turn the way you do with a DG (turns on compass alone have to be timed).
If this is a big enough problem, vertical card compass units are pretty common now, so the compass presentation is the same as the DG's, just like in the good old days, but easier to follow.

Very interesting, thanks for your answer :)

Both Dan and John are right. This exact thing has confused me, too. Especially when using the track (heading) indicator or VOR on a Garmin G430 Which looks similarly to the old school drum style Directional Gyro that John K describes, but turns in the direction you would intuitively expect. That is because there is a difference in the way that a vertical compass card works and is read versus the way an old school aviation compass works and is read. And, I call them old school even though I have seen them in brand new Piper Archer IIIs and relatively new[ish] Cessna 172SPs.
Vertical compass cards work using flux gates that can align themselves with North regardless of compass orientation. Old school aviation compasses like float or whiskey compasses work using a North-seeking magnetic bar or needle. This needle embedded in the body of the float. When viewed from the top, the North-seeking end of the needle is furthest away from you when you are facing North. But, if you can only view the float from the side, which is the case for a float compass, you can only see the side closest to you. Everything is reversed in the case of a float compass.
Try this. Take a can, a cup, a lid, or some type of cylindrical surface. Draw a compass rose on its top. Orient the compass rose to your local Magnetic North. Now, position the Cylinder so that it is between you an the magnetic North Pole while maintaining its Magnetic North orientation. This means you are also facing North. This will require you to put the cylinder in a position where it does not move. With the cylinder at eye level, and positioned between you and the North Pole, write the letter “N” on the side closest to you. Now, walk around the stationary cylinder until it is East of you. This means that you are a West if it. Yet, you are facing East. Write the letter “E” on the side closest to you. Do the same for West and South.
You will quickly see that, while the float compass is moving in the correct manner to keep it aligned with Magnetic North, your perspective on its movement is reversed. A CFI once told me, “Whiskey compasses are like women. If you want one to come to you, run in the opposite direction.”


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What is the best way to give ATC a position report using only a VOR (no DME or GPS)?
While cumbersome, is it permissible when asking for a pop-up IFR clearance to state, at the intersection of WWW radial XXX and YYY radial ZZZ?
Obviously, during VMC, you have your pick of visual checkpoints, but in IMC, are there any better suggestions?
Additionally, if you are near a navaid or published intersection, and take a guess at your distance from it, how far off would your guess have to be before ATC wouldn't really even consider it helpful?

I'm going on the assumption you're operating in IMC (or perhaps VMC above a cloud deck) and have no reference to the ground. In a situation if you need a pop-up IFR clearance or ATC is requiring you to provide position reports for some other reason (non-radar, or your transponder is dead and they want to identify you but don't have time to issue you confidence maneuvers).
I'm going to further constrain the scenario with the assumption that all you have are "basic" IFR instruments (6-pack, clock, compass, and VOR -- no VFR/Handheld GPS, DME, or other fancy stuff).
The AIM has some guidance on this subject in 5-3-2, but the general idea is your report should be "as accurate as possible". For routine position reporting like you'd use in non-radar environments (where you're giving an estimate of when you'll reach a reporting point) they're looking for "within 2 minutes flying time" on your estimates in most situations, so you'll want to give your position with the same sort of accuracy.
In the case you describe, with no DME, GPS, or other precision tool for reporting your distance and bearing from a fix your the most accurate option would be to report crossing a published intersection, VOR, or other reporting point noted on your chart - it's the most definite "I am HERE" report you can give, and ATC will certainly know the location.
If that's not an option (ATC needs to know where you are right now, and you're not over a VOR or charted intersection) I would probably start by computing the distance using the intersection of two VOR radials (whether this is a charted intersection doesn't matter, though it would help if your report is relative to one): Break out your chart and mark the location, then take your ruler and measure the distance from one of the stations (or a nearby intersection along the airway you're using) and you've got your position "as accurately as possible".
If you don't have a chart or can't get signal from a second VOR for some reason it's time to work out a time/speed/distance problem in the air:
If you flew over ABC VOR 10 minutes ago and are now flying from the VOR on the 090 radial at 120 knots, and you've got a 20 knot headwind (which you know from the Winds Aloft forecast, updated with data from previous position and time/speed/distance computations) then you know you've traveled about 17 miles, so you're "17 miles from ABC VOR, on the 090 radial".
The time/speed/distance computation has a lot of potential error (winds not as forecast, for one), but sometimes it's your only option.

Press the NRST button on your GPS, and give them the distance/direction from the fix:
"5-4-XRay is 7 miles southeast of K-A-S-H"
Just because you are /U, it doesn't mean you can't use a VFR or handheld GPS for non-navigational position reporting. If you're IFR and don't yet, in 2015, have a an IFR or VFR GPS, or a handheld GPS running an aviation app in the cockpit, you should turn in your ticket.

GPS is a wonderful tool - I usually have a portable GPS running when I'm flying, but usually is not always: There are days I go up with paper just for the fun of staying proficient with it. Also sometimes my portable GPS loses signal (yes, that does happen) and becomes a glorified electronic chart with no working "Nearest" button…

In most cases GPS is a good solution, but there are regular outages (announced by NOTAM); there was a very high-profile one affecting Superbowl traffic this year and the 'workaround' for arriving IFR traffic was VOR navigation. Back to basics :-)

@voretaq7 OP asked about an IFR popup, and I wrote: "If you're IFR..."  You wanna bang around VFR with paper and a watch, like I do, go ahead, but that's a different question.

@Pondlife i'm sure most of the affected Super Bowl traffic was /F, not what OP asked about

What's /F? But anyway, my point was that any answer that amounts to "just use GPS" is a little oversimplified, especially for IFR.

/F is an equipment suffix for area navigation. an FMS, for example, is /F, and it doesn't need a GPS to provide position on a moving map.

I believe Don Brown ranted about this, people giving him references from their shiny GPSs, only problem was he didn't have those smaller airports on his (artcc) scope and they couldn't give him a position relative to the major VORs in the sector.

That's why I picked an airport with a long runway and an ILS.

That would be acceptable to me, but probably more information than you need to give.
If you have a transponder, we'll give you a squawk code (and perhaps ask for an ident as well) and radar identify you that way. We will then call "radar contact" and advise where we think you are ("two-eight miles northwest of Podunk VOR"). If you don't have DME you won't be able to cross-check the milage but you can at least confirm you're on the 340-ish radial and be confident the controller knows exactly where you are.
In this situation the position report is useful so the controller starts scanning the appropriate area of the scope. If you're in an area where sectors are relatively small, e.g. in the terminal (TRACON) environment below 10000 feet or so, there aren't a lot of places you could be and an exact position report isn't crucial. Even if you don't have DME, you can look on your map and see that if you're on these two intersecting radials then you're in an area approximately twenty to thirty miles northeast of Podunk and you tell us that—and that's fine. If you're calling a center controller whose sector might be upwards of a hundred miles or more in either direction, the position report becomes more important.
For this method, if you think you're near to a named intersection/waypoint, giving a position relative to the waypoint is just as good as giving it relative to a VOR. Well, probably just as good. Depending on how well the controller has their airspace memorized.
If you don't have a transponder, an accurate position report is one way of establishing radar identification. In conjunction with the report you also need to tell us your heading or route of flight. We look and see if there is a single target in that area on that heading and radar identify you that way. If you don't give us either piece of information, or if there are multiple possible targets, we can issue an "identifying turn" of thirty degrees or more and observe a single target make such a turn and thereby identify you.
For this method you would probably want to be pretty close to a defined waypoint in order for it to be useful to identify you based on position report alone. Say within a mile or three, for a TRACON controller. A center controller will be zoomed out more; if you're the only target in the vicinity you might get away with five or ten miles, maybe.
For your information, at least in the terminal environment, there is a command we can enter to draw a range-and-bearing line on the scope from any target, or from a defined VOR or intersection, or from any clicked-on location, to any other target/fix/location. If you give a position as the intersection of two radials we would be able to draw those radials on the scope and see where they intersect. But that might be more work than a controller is willing to do unless they're having a really hard time finding you.

You don't say whether you talking about center or a tower. I would definitely never give a tower such a position. If I was talking to an ATCSCC, maybe in wierd scenario (broken transponder for example), but in all honesty it is the pilot's job to have charts and report position properly. Trying to get a controller to pull out a chart and compute your position is not a good idea, and I doubt they would cooperate unless it was an emergency.
In real life, what happens when you don't know your position, is that you would have the controller find you with radar, so you just say "Boston Center, Cessna November 54321", and center will answer "Go ahead November 54321", then you say "November 54321, what is my position?" and control will say "Ident", then you push a button on your radar transponder. This causes a "blossom" on the controller's radar screen and he can see exactly where you are. The controller will then give your position to you.
Note that this often happens even when you accurately report your position. So, for example, you might call in "Nashua Tower, Cessna one seven two November five four three two one, six miles west of water tower, maintaining three thousand five hundred, with information Romeo", then tower might say, "November five four three two one, ident", then you push the button. Then, they will know exactly where you are.

The intersection of an arbitrary pair of radials definitely isn't appropriate (which is what I think you're saying here), but charted intersections (or computed distances from them) often are - particularly ones on an approach chart for the airport (hopefully tower controllers know their own approaches, and if not they should have access to the chart!) Your answer doesn't currently make that clear & by my read it implies that such a report would be inappropriate.

We ask for an ident even after getting a position report for two reasons: 1) the fix you're using must be displayed on our scope (a visual reporting point may or may not be); 2) you need to give both your position and heading or direction of flight in order for us to radar identify you based on just a position report. And @voretaq7, it might be cumbersome but at least in the Terminal environment (STARS) we would be able to get a decently accurate fix if you told us you were at the intersection of the ABC123 and XYZ321 radials. We have a function that can draw lines on the scope from VORs.

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text:
Can ATC decide whether or not to provide tower enroute services?
Recently, when I requested tower enroute service from a Southern California airport with published TEC routes, I was told by the controller that, out of courtesy for him, I needed to prefile.
If I wanted to push the issue, would the regulations have been on his side, or mine? What good is TEC if it has to be prefiled?

According to the AIM, 4-1-19-c:

There are no unique requirements upon pilots to use the TEC program. Normal flight plan filing procedures will ensure proper flight plan processing. Pilots should include the acronym “TEC” in the remarks section of the flight plan when requesting tower en route control.

Based on that, it would seem that the TEC request was essentially equivalent to that of getting a pop-up IFR clearance. If you pre-file, the controller has all the information necessary to enter you into the system rather than asking for it over the radio. It wouldn't be legally required, but neither would the controller be required to issue a clearance if workload doesn't permit.
When using a TEC route, there is still the benefit of only talking to local controllers, and using a known routing that you're less likely to have amended.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
How is thrust vectoring controlled by the pilot?
Thrust vectoring is used to extend the manoeuvrability of aircraft outside a `normal' flight envelope, by providing (optionally differential) vectored engine thrust, as explored in many previous questions (this and this).
How is the direction of vectoring actually controlled by the pilot during flight? Does a flight control computer automatically interpret "traditional" control surface inputs under extreme conditions and move the nozzles appropriately to create the desired effect? Or is vector direction a separately controllable interface?
I've noticed in my flight sim of choice, XPlane, that the configuration panel allows the mapping of an analogue axis on my joystick/pedal setup to 1D vectored thrust. I've no idea if this is representative of any real fast jets, but if it is, it seems that this approach could create a lot of extra "pilot workload" -- given that it's another one (to three!) control axes to be manipulated -- and manipulated at the same time as pulling potentially very aerobatic manoeuvres with little room for mistakes. This seems like a Bad Idea.
On the other hand, it might be the case that independently controlled vectored thrust allows for a wider range of aircraft manoeuvres than that which could traditionally be 'expressed' by control surface movements alone. Giving fast jet pilots the extra workload would, therefore, be worth the risk.

On most airfcraft with thrust vectoring, the pilot doesn't even control the aerodynamic control surfaces, so my guess is, she doesn't control the thrust vectoring either. Heck, on modern high-performance jet planes even without thrust vectoring, all the pilot does is express to the computer what she wants the airplane to do and the computer figures out how to do it. You probably wouldn't expect a pilot to control the Flowers Of Steel any more than the Valse des Ailerons.

A long talk about F-22 controls by a test pilot: https://youtu.be/n068fel-W9I (the gist is that side-stick and pedals tell the computer what the pilot wants and the computer combines all the available control elements to achieve it).

Thrust vectoring isn't controlled by the pilot directly, except being able to turn it on or off in various circumstances. If it is on, the aircraft computers control the vectoring based on external conditions, the state of the aircraft and control input.

This. Thrust vectoring is under control of the "fly-by-wire" system present in all such jets, and is utilized to do what the pilot indicates he wants through input on the stick and rudder pedals, combined with information about the aircraft's current airspeed, angle of attack and attitude; thrust vectoring typically only kicks in for extreme aerodynamic maneuvers and/or post-stall maneuvering at low speed or high AOA.


text:
What is the most overlooked item during preflight inspection?
Have there been any studies that gathered statistics on overlooked items on preflight inspections, or even statistics on how many pilots actually perform a good preflight (following a checklist, etc.)?
If such a study exists, did it uncover anything that proved to be something that was often overlooked?
Is there an industry "best practices" document for preflight inspections (beyond just following the manufacturer's checklist found in the POH)?

The corollary would also be interesting too, how many perform a postflight inspection, or even follow shutdown checklists? I regularly charter a plane at a local FBO and it's not uncommon that it's sitting in the hangar with the flaps down (first item on the after landing checklist, flaps: up, makes you wonder what other items they didn't do)...

Yeah, I'm wondering if there has been any formal studies that would move it from anecdote to something more concrete. I have a feeling postflight inspections are rare, but I wonder if there are some numbers to that. Also, I'm looking for ways to improve safety that go beyond following a checklist. Something someone told me once was to "rock the wings" while performing the preflight and before sumping fuel, as that would dislodge any water from behind wrinkles in the fuel tank. Something that I've added to my preflight but you won't find on a manufacturer's checklist.

For light GA aircraft, based on how often we seem to have fuel exhaustion incidents, I'd say the part about "Look in the tanks to see how much fuel you have" is overlooked far more often than it should be.

@voretaq7 yep. I visually inspect the fuel level every time!

@Canuk Wouldn't mixing up the water and fuel right before sumping potentially cause you to miss water in the fuel? Sumping works because water (being heavier) settles to the bottom of the tank, but if you mix it up right before sumping, couldn't that cause you to miss it?

@reirab It's a pretty gentle rock of the wings, I'm not like shaking it so hard it re-homogenizes the water/fuel. I also do it as the first thing when I walk up to the airplane and by the time I get to checking the sumps, if it did mix, it should have re-settled to the bottom.

@Canuk/reirab- I am a wing rocker too! often the planes I fly are left over night with half empty tanks (so prone to condensation) ... so i rock the wing at the start of my preflight ... hoping(!!) that as you say that by the time I get to the sumping, and then again at refueling water has settled -

This FAA article is about using electronic checklists for airline flights (it concludes that they're better than paper ones) and includes this quote:

They found the crews averaged 3.2 checklist errors per flight (one of
  the observed flights had 14.) The most-common checklist error involved
  the omission or deferral of an item, which was later forgotten.

NASA commissioned a general study into checklists in 1990, but it doesn't identify specific items that are commonly overlooked. It does say that as the number of items on a checklist increases, the chances of overlooking any individual one does too:

Swain and Guttman (1983), in their study of nuclear power plant
  operations “recognized the fact that as the list of items grows, there
  may be a higher probability of overlooking any given item” (chap. 15,
  p. 13)

The final section of the paper has recommendations for checklist design, which could be considered the "best practices" you mentioned, but of course it's a very general list, e.g.

The most critical items on the task-checklist should be listed as
  close as possible to the beginning of the task-checklist, in order to
  increase the likelihood of completing the item before interruptions may occur

AOPA's Flight Training magazine has an article on "frequently forgotten" checks that is more specific and most of the checks seem to apply to most (light) aircraft, but it doesn't provide any authoritative sources. They also have a "how to preflight" article that gives more information and includes this interesting observation:

As an experiment, I held a preflight contest with a "bugged" trainer.
  I reversed the rigging on the ailerons so their movement was contrary
  to control inputs. Every one of the contestants checked control
  movement and freedom, but no one caught the problem.

Putting all that together suggests - only to me, and I'm not an expert - that it's less important to think about specific items that you might forget, and more important to ensure that you complete the checklist fully and really verify the results of each check. If you consider some checklist items to be 'more important' than others then it could also lead to mistakes because you overlook the 'less important' ones.

Thanks for the great, well-researched answer.  It appears to me that it's not one particular item that gets overlooked, but rather a habit or distraction that can cause something to get overlooked. I particularly like the idea of the important items at the top of the checklist.  I also found an interesting book that talks about the phsycology of creating checklists that was fascinating: "The Checklist Manifesto" by Atul Gawande (http://amzn.com/0312430000)


text:
Do the captain's and first officer's rudder pedals always move together?
I worked on Russian Fighter aircraft where both the Rudder Pedals were mechanically interlinked i.e Captain applies force on his pedal than both pedals (Captain & First Officer) move & vice versa. Single Pedal sensor Unit (of course redundant sensors) senses the position and sends it to the Fly-By-Wire Computer for moving the control surfaces.
I would like to know if this is true for all aircraft (Fighter/Commercial, Boeing/Airbus, etc.) and if not, what are different implementations? Maybe different sensors for Captain/First Officer, different arch etc.
Also on the same lines, how does Pedal Feel operate i.e, does it takes a signal from pilot pedal sensor or from actuators to provide feel to the pilot/copilot?

I can't speak for all aircraft, but I'm pretty sure I read something about them being interconnected on the A320, which would be my "usual suspect" for "independent flight controls to confuse the heck out of the pilots" design. (Presumably like on the fighter aircraft you describe there is a single/redundant sensor unit to determine their position and "politely request" that the computers move the rudder as directed.)

@voretaq7: yep, there have been issues where the PNF has been resting their feet on the pedals and obstructing the pilot flying. On the A320, during flight control checks the PNF is meant to "follow" the pedal movement while the captain tests the rudder.

@Qantas94Heavy; this is part of the reason for checking for free control movements. It's less of an issue with a PNF, since they generally know what's going on, a passenger occupying the right seat might not however.

@voretaq7, in A320, rudder pedals and elevator trim are the mechanical backup, so they have direct hydraulic connection to the rudder. The other Airbus models have different backups though, so it might differ there (I have only read documents for A320, so I don't know the details for the other models).

I am curious about a fighter aircraft that has two pilots. Do you have a model name?

In the EMB-145 and -135 the rudder controls are mechanically linked in the tail in an assembly that converts torque from the rudder cables to linear rod input into the rudder hydraulic control units.  Up until this assembly the rudders are technically independent and the cables for each rudder are routed differently through the airframe so that a single point of damage does not render the rudder inop.  The autopilot servo is only located on the captains rudder cables.  Through the rear linkage both pilots rudder pedals will move together when either provides input.
Our other controls are a bit more interesting.  The roll input is also linked, but it is linked at the control column,  Each yoke independently controls its own aileron -- the CA yoke only flies the left aileron and the FO yoke the right aileron.  It is only through the control column linkage that each yoke can control the whole airplane.  It is done this way so that if there is a problem with a cable jamming, the control interlock can be disconnected and at least half control regained.

All? I doubt there's anyone who knows all models of aircraft but it seems the norm at least.
How they operate depends on the aircraft of course. Anywhere from fully mechanical, direct linkage to the rudder through cables to directly driving hydraulic pumps that drive the rudder to driving sensors that feed data to the flight control computers which in turn drive electric motors that drive the hydraulic pumps that drive the rudder.

Well, there could be a safety requirement for the pedals behaving this or that way, then all the aircrafts would behave very similarly.


text:
If the landing gear is stuck in an airliner, can the crew go down and manually open it?
There are several instances where we see the landing gear getting stuck before landing. In these kind of situations, can the crew, or one of the pilots, go down to the landing gear area and solve the issue?

Depends on the plane, there is usually a manual release for the gear but if that fails it'll be a belly landing.

For some reason, this comes to mind: https://www.youtube.com/watch?v=JlSQAZEp3PA

I was thinking of this situation https://www.youtube.com/watch?v=ANLgWY6I9uk but it also depends on the plane and altitude although it would be assumed you would be low and slow for a maneuver like this.

@Dave - I remember that incident when it was a bit newer. It took a couple of tries, but they got it, saved the plane and possibly the pilot's life.

@Dave. Woah! That's pretty stinking impressive!

@Antzi - Though the guy who pulled the gear down into place (Jim Moser) knew the pilot (Scott Gordon) from work at air shows doing stunts like landing aircraft on truck beds, which is how they got the idea to fix the problem this way, both of these men insist the St. Augustine incident was a real emergency situation, no pre-planned stunt.

@KeithS sorry, I thought this was https://www.youtube.com/watch?v=FoSGzLii0KM I redacted my comment since I don't know if it was fake or not :)

To me this is not a duplicate: this deals with mechanical block, the other with actuator power loss.

Why this is suddenly marked as duplicate, after such a long time. And this is a different question.

This is not a dupe, it is considerably less specific than the other question.  Not too broad for the site, just more broad than the supposed duplicate question.

On older (WWII-era) large planes, the crew had access to a manual crank to lower the gear if the automatic extension/retraction system (usually a linear actuator powered electrically) failed. I don't know of any that had a gravity-based manual system; I'm sure a few bomber crews would have appreciated something like that after having to crank the handle to get a disabled main gear locked. Here are the manual crank ports for the B-17, on the forward bomb bay bulkhead with red arrows indicating the direction to crank:

The B-17 had a retractable tail gear as well, so there was a third manual crank in the tunnel to the rear gunner's position (but if there were multiple gear failures, the main gear would be the priority).
On more modern airliners with hydraulic extension/retraction, manually cranking the gear into place isn't as much of an option (especially since any access to a crank linkage would be in either the passenger cabin or the cargo hold). For these aircraft, the gear are designed with a "manual extension" or "gravity release". This basically disconnects the gear strut from its uplocks and the hydraulic cylinder, allowing gravity to pull the gear down and then momentum (or a spring mechanism) will engage the downlocks. Here is a diagram of the 737's manual gear panel on the right-hand wall of the flight deck:

The 747 has a manual nose gear extension system in the avionics compartment below the first-class cabin. The 747's main gear are much more complex, but it is still possible to let gravity pull them into place, by using a set of "alternate gear extension" switches on the overhead panel to release each gear from the hydraulics and uplocks:

It doesn't always work; a Virgin Atlantic 747 pilot was forced to make an emergency landing with the outboard right main gear stuck in a half-extended position:

This question does seem like a duplicate but I think your answer is much better than any on the original question.

The 727 has a manual crank extension system.

There have been cases where the gear would not extent and the pilot opted for a "gravity" release. However this sometimes also does not allow for the gear to click in place. The pilot can than perform a few higher g than normal pull ups to lock the gear securely.

@Brilsmurfffje - True. I also remember a fairly harrowing situation in which a small plane's gear was jammed, and the solution was to have the pilot come in low over the top of a truck, with a guy in the bed to pull the gear down into place. It worked, everyone was fine, but so many ways that could have gone wrong.

Did the flight land safely?

No, there isn't.
I don't think any aircraft has access door from inside to the main wheel well. Some aircraft do have access hatch via the nose wheel well, but since the wheel well is unpressurised and the cabin is pressurised, it would not be possible to open the hatch in flight and even if it was possible (after depressurising the aircraft at low altitude), trying to do anything there with the gear door open (which it would have to be obviously) would be extremely dangerous and the chance of success would not be big, because a man has much less strength than the hydraulics that already tried to get the gear out and failed.
Any aircraft with retractable landing gear is required to have an alternate extension mechanism that can be used to extend it if the primary system operating the gear fails, which was already well explained by KeithS. But when that also fails, there is no way to access the gear to attempt to unjam it.
Aircraft are designed with all sorts of emergencies in mind and even landing with partial gear is not a big deal. Sure, it will do some damage to the plane, possibly even to the point that it's not economical to try to fix it, but that's what insurance is for, and risk of injury is minimal. For recent examples of gear mishaps see:

Jetblue A320 at Los Angeles on Sep 21st 2005, nosewheel tilted 90 degrees for landing and Vueling A320 at Sevilla on Apr 20th 2011, nose wheels tilted 90 degrees on landing
Wizz A320 at Rome on Jun 8th 2013, left main gear did not extend and Alitalia A320 at Rome on Sep 29th 2013, right main gear did not extend
LOT B763 at Warsaw on Nov 1st 2011, forced gear up landing

All occupants of those aircraft were OK, only 3 minor injuries in one of them from the evacuation.
Also in some cases the gear fails when the aircraft touches down, so nobody could do anything about it, because there is no indication it's going to happen beforehand. If it's just that, the risk of injury is still small. Example:

Ariana Afghan B734 at Kabul on Nov 7th 2014, gear collapse on landing

which also ended without injury.

authors: Ольга Невская


text:
What are the reasons to evolve from trim tabs to moving the entire surface (e.g. stabilizer)?
Modern commercial aircraft use stabilizer to trim instead of trim tabs. What are the advantages and disadvantages of this design choice?
Have aileron trim and rudder trim evolved in a similar way to move the entire control surface rather than aileron / rudder trim tabs?

"entire surface" is usually used for the all moving tail (or canard) plane that supersonic aircraft have where the surface moves as single piece. While trim using movable stabilizer (as most airliners have) means the surface is still composed of two parts and both move independently.

Trim is used to zero the stick forces at the desired flight condition, and with the small, slow early airplanes, an adjustable spring somewhere along the control cables would do. When speed increased, trim tabs were introduced, because their trim force goes up and down with dynamic pressure, whereas the spring would always create the same force. This would require re-adjustment with every speed change.

With the increasing size and speed of airplanes, manual control required ever more complicated means of force reduction (Flettner tabs, spring tabs), and the relative chord length of all moving surfaces shrank to allow for more control with less force. The moment around the hinge of a control surface increases with the square of the chord, but the lift change for a given deflection angle increases only with the square root of the chord.

In parallel, wing loadings increased, which required high-lift devices to keep take-off and landing speeds down. These add a lot of lift in the rear part of the wing, creating a strong nose-down moment, and now a simple control deflection would not suffice to trim the airplane. The reduced chord length meant that high deflection angles would have been required for trim, reaching far into the region of deflection angles with declining effectiveness. That is when adjustable stabilizers came up: The trim change with all configurations was simply too big to be covered by the elevator alone.

Transsonic flight was next, and here the adjustable tail incidence is crucial to trim the aircraft trough the transition from subsonic to supersonic flight. A contour break from a deflected elevator could cause shocks which could produce elevator reversal. The dynamic pressures of jet flight put an end to manual control - the last, famous examples were the Canberra or the Dash-8 (Boeing 707 prototype). Now hydraulic actuators were used, but still it makes sense to use aerodynamic means to reduce control forces, because the size and power requirements of the actuators can be reduced with clever hinge moment reduction. The trim tabs were initially moved by cables, but soon they used electric actuators.

Since rudder and ailerons are not affected when the high-lift devices (Fowler flaps, slotted flaps) are deployed, they still use simple trim tabs. Newest developments are electric control surface actuators which can help to save mass and avoid the messy hydraulics. The RQ-4 uses electric actuators because the hydraulic fluid would have to be pumped continuously through the lines in order to keep it warm enough at the high operating altitude. Only the landing gear still uses hydraulics for retraction.

I'd say that it was the widebody that put the true end to manual controls -- DC-9s (all the way up to the last B712 that rolled off the lines) still have manual cable-and-tab controls for most things...agreed that you need a movable tailplane of some flavor for transonic flight, though.

@UnrecognizedFallingObject … but I bet they had boosted ailerons. The real art is to design ailerons such that no force multiplication is required. That was what I meant with "manual control", but of course you are right, a boosted manual control is still a manual control.

the DC-9 ailerons are aerodynamically boosted, but require no hydraulic boost.

One reason for moving the entire surface for trimming is efficiency. Deflecting the elevators or trim tabs creates more drag than adjusting the whole surface. The control surfaces are more aerodynamic without trim tab deflection.
The elevator is the main surface needed for trimming the aircraft. This is because things like fuel and payload will affect the center of gravity (CG), and the elevator is trimmed to balance the airplane. In addition to this, the external loads on the aircraft change throughout the flight from things like thrust settings and lift and drag from the wing. Different airspeeds and extension of flaps, speed brakes, landing gear, etc., will also affect the balance of the airplane.
Balance left and right is less of an issue, and can be addressed by changing the balance of fuel between tanks. Aerodynamic forces tend to stabilize the aircraft in yaw, so trimming in yaw is really only an issue in rare circumstances. Rudder or thrust settings can be used to adjust as necessary.
Another reason is the structure of the airplane. The horizontal stabilizer has much less load on it than the wings. The ability to move the tail surface adds weight and complexity to the design, and this would be a much greater challenge with the wing. The efficiency benefits make this design feasible for the horizontal stabilizer, but there aren't enough good reasons to move the vertical stabilizer or the wings to justify the costs.
Aircraft that actually use the entire stabilizer surface for control are in a different situation. These are generally military aircraft that need to maintain high maneuverability, especially at very low or very high airspeeds (see this question). These aircraft are also generally smaller, so moving a smaller surface is less of a challenge.

Flap deflections up to 10° do not increase drag, but add camber. This increases the maximum and minimum lift coefficients of a flapped control surface, which in my eyes make it aerodynamically better than a full flying surface: It can be smaller. Nothing reduces drag like less surface area.

Trim tabs let the pilot move the control surface more easily. It is the elevators that actually affect the plane's attitude.
A all moving tail gives more control over the attitude compared to just the control surface. They also allow for more control in stall and transonic conditions (during flow separation) because the pilot can control the leading edge.

Not all trim tabs reduce control forces. Take the elevator of a DV-20 Katana: It moves such that control forces are increased.

Advantages of full moving surfaces include:
1. Less drag
2. More authority
Disadvantages include:
1. The control surface can stall.
2. Requires move structure and more force to move.


text:
Why is stabilizer trim often controlled by electric motor while other surfaces are mostly hydraulically controlled?
What is the rationale behind the use of electrical motors instead of Hydraulic actuation for the stabilizer which I have seen in most aircraft like Boeing 787.

Most trim is either manual or electric. Trim changes do not have to be quick, but should be precise. Control surfaces like the elevator must be able to move quickly, so big aircraft use hydraulics for that.

Many aircraft do use hydraulic stabiliser control (I know the DC-10 and A320 do off the top of my head).

Weight, cost, reliability and maintenance.
See ACTUATION SYSTEM DESIGN WITH ELECTRICALLY POWERED ACTUATORS
Safety
See THE A380 FLIGHT CONTROL ELECTROHYDROSTATIC ACTUATORS, ACHIEVEMENTS AND LESSONS LEARNT

In terms of safety several aspects can be
highlighted: As far as power source redundancy
is concerned the number is increased from 3 to 4
since 2 electrical systems replace 1 hydraulic
system. Furthermore an additional margin of
safety results from the introduction of the
hydraulic/electric dissimilarity in the power
sources: This provides further protection against
common failures, such as maintenance errors,
which may affect all the hydraulic systems,
whatever their number. Moreover the electrical
power provides flexibility in routing, resulting
in an easier segregation of power distribution
routes against engine burst and other “particular
risks”, and an isolation and reconfiguration
capability that hydraulic systems cannot offer.

The reduction in the total number of hydraulic
components results in improvements of the
MTBF and dispatch reliability, by elimination
of potential leakage sources.

The elimination of the generation and
distribution components associated to one of the
hydraulic systems (pump, reservoir, filters,
plumbing…) and the replacement of the
associated hydraulic actuators by electrically
powered actuators results in weight savings.

Could the plane (DC10?) that lost all hydraulics perhaps have landed better if electric trim tabs had been available and functional?  My impression is that it landed very rough because there was no way to stabilize the fugoid oscillations using only thrust controls, but I would think being able to adjust trim might have made it possible to find a setting where oscillations were substantially damped and controllability thus improved.

Hydraulics are used if you need to move something large quickly. Also, hydraulic actuators are perfect for linear motion, whereas electric motors are best for rotary motion. On the other hand, electric motors can be controlled more precisely: By counting the number of revolutions and the angle of the shaft, an electric motor can drive the trim spindle much more precisely than hydraulics, which move fluids into cylinders at high pressure. This does not (at least easily) allow for feedback on the position of the actuator, and only a limit switch can give easy position feedback.

In order to move a number of control surfaces, with hydraulics you need only one pump. Normally, only one surface is moved at a time, so it can use the full power of the pump. Together with a pressure reservoir, this allows for large forces and large strokes. If you wanted to get the same control power with electric actuators, each control surface would need to have a big electric motor and gearbox next to it.

However, hydraulics are messy (can leak) and more maintenance-intensive than electric actuators. Hydraulics are less energy efficient (after all, all those lines create a lot of internal friction drag) and at low temperatures, the oil must be circulated continuously to keep it warm and "runny". That is why electric actuators are now used in applications which had traditionally used hydraulics.

Drag is everywhere: internal friction drag :-)


text:
Why are predator drones being used over civilian California?
A couple of months back I was going on a road trip through California and stopped by a dry lake called El Mirage Lake. It's a very tacky area requiring a permit to enter.
My friend and I showed up near midnight and could hear a VERY low-flying aircraft. I happened to have a flashlight with a 800 m beam distance and using it we could clearly see a Predator drone less than 500 feet over the ground.
The drone was flying an autonomous rectangular course over the lake all night, but the next morning it had changed altitude and was flying a few thousand feet over the lake - high enough that it just looked like a normal airplane.
For 30 minutes or so there was a Cessna following behind it which was very strange... Would it be a human monitoring the drone for some reason?
Anyway, as a current civilian I feel like there's something wrong with military aircraft being used as surveillance over public area, not to mention it seems a little pointless. Why is the government (or at least state of California) using equipment like this for useless reasons?
I have a pretty bad photo of it using a telephoto lens that I can post later as proof that is was actually a Predator drone.

Similar incident: http://aviation.stackexchange.com/questions/7426/what-is-this-object-that-followed-me-up-the-street

You're making a huge leap from "I saw a Predator flying" to "The Predator was on a surveillance mission against the American people."

And worse, assuming that such surveillance would be useless. I can see definite benefits of using UAVs with IR scanners for detecting things like marihuana groweries (right now manned helicopters are used for that, UAVs would have more endurance, lower cost, and be less noisy).

@jwenting Well, currently medical marijuana is legal (so it can be grown legally) in 20 states, incl. the OP's) and it is legal for recreational use in 2. Of course that would not stop the Federal government from performing those type of flights. (and yes, I understand that medical m. use would not need a field or fields worth of pot. :) )

@CGCampbell it's legal here to have up to 5 plants, police do the flights regularly because many people end up turning their attics into professional greenhouses, complete with high power lights, dripfeeding water systems, and CO2 injection, all without proper electrical wiring and often with stolen electricity (and growing dozens of plants that way). Just in the last few months they rolled up at least 2 operations within about a quarter mile of where I live that way.

Ahh, I don't know much about the whole lifestyle, my job would not let me ever indulge, even if it were Federally legal.

@DavidRicherby While in this case it appears to be test flights, IIRC, (unarmed) Predators are actually used domestically from time to time by law enforcement, border security, and other such situations (including forest fire monitoring) where their ability to loiter on target for a long time to surveil an area is useful. My favorite article on this topic was when Arizona had requested more of them to patrol the border... the article was named Aliens vs. Predators. :)

Once I was near a supposedly civilian airport and in amongst the Airbuses, I saw a parade of C-40s, C-32s and KC-767s flying in, even a C-33, which you can't mistake for anything else!  Worse it appeared some had been faked up with civilian markings. The government is up to something.

@Keegan --" It's a very tacky area "  (1 : not having or exhibiting good taste: such as. a : marked by cheap showiness : gaudy a tacky publicity stunt a tacky outfit. b : marked by lack of style : dowdy.)  "requiring a permit to enter" -- huh?  There seems to be a disconnect here.

An article from 2001, TESTING SPY PLANES GRAY BUTTE AIRFIELD TO BE REOPENED says,

General Atomics, which makes the Predator in San Diego, has been conducting final production tests and checkout flights at El Mirage, three miles inside the San Bernardino County line.

See also EL MIRAGE FLIGHT TEST FACILITY

But this is 13 years later... How does this answer the question?

13 years later, they're still manufacturing them and still test-flying them?

Because they still need to test the planes built to the old design as they come off the production line, they still need to test any changes to the design and (though it sounds like this isn't relevant to the situation you describe) they still need to train new pilots.

They might also test-fly every drone (or every 10th, or one in every batch) for quality control purposes

ChrisW's answer covers "why the Predator?" (El Mirage Field is used by General Atomics for test-flying their drones), which makes "Why the Cessna?" easy to answer: if General Atomics is test-flying a Predator drone or variant, the Cessna is probably there as a chase plane to monitor the test.

In fact, a quick search turned up multiple images of Cessna's used by GA as chase planes.

I'm pretty sure (can't find proof) that any UAV operating in US domestic airspace must be accompanied by a manned aircraft.

@egid I seriously doubt that. Maybe if it didn't have a civilian rated transponder and was not operating under military rules. But the USAF has been operating unmanned aircraft without chase planes for decades (often as target drones).


text:
What charts do I need flying VFR between KPRC and KLAS?
Some friends and I are going to fly up to Vegas from college to watch the Red Bull air races in a few weeks.  And after looking at the charts, I realized I am in a pretty unique situation.
The Phoenix sectional ends just short of Vegas - so normally I would buy a Vegas sectional.  However, the KLAS TAC extends just into the Phoenix sectional.
Should I buy the Vegas sectional as well, or can I just use the KLAS TAC once the Phoenix sectional ends?

Do you absolutely have to use paper charts? There are many apps available for tablets that provide the charts for free, which is a lot more practical in many cases, although of course you may still like to have paper as a backup.

Unfortunately I do have to use paper, I would love to use a tablet though... just not in the cards right now.

OK, thanks for clarifying. Then as voretaq7 suggested I would take the TAC because it provides more detail.

If I understand correctly, your question is "can I substitute a TAC for a sectional on a cross-country flight?" However, assuming that you're flying under part 91, there is no legal requirement to have any charts on board at all. 91.503 does require them, but only for large and turbine aircraft, and the FAA has stated that electronic charts are allowed instead of paper.
There are a few places where it is required to carry a chart in the aircraft, per the Special Flight Rules Area regulations in 14 CFR 93. Some examples are:

Near Los Angeles International Airport (93.95(c))
The Hudson and East River Exclusions in New York City (93.351(d))

So unless 91.503 or one of the part 93 rules applies to your flight, legally you can carry whatever paper, electronic or hand-drawn charts you like - or none at all - although if you bust restricted airspace and the FAA come after you, not having charts on board may not look good. (Of course, if you do have them then the implication would be that you didn't use them or don't know how to read them, which isn't good either.)

Thanks for the answer.  I do understand that I "don't need charts" but I was looking for 'insight' from a more experienced pilot than myself - and what they would do in the same situation.

@KeeganMcCarthy Well, for what it's worth, I use Garmin Pilot on two separate portable devices for both VFR and IFR, with no paper backup, which is in addition to whatever is actually in the aircraft: either G1000 or G430. I feel comfortable that that gives me enough redundancy and I don't miss paper at all, but others may feel differently; 'insight' and 'opinion' are tough to separate.

@KeeganMcCarthy Like Pondlife I just use an electronic flight bag (in my case, Foreflight on my iPad, and my iPhone as a backup). If you want to carry paper charts the TAC is certainly adequate if it covers your intended route/area of flight and you can use it as you describe in the question (in fact I would do this simply because the scale on the TAC provides more detail - particularly if you're not familiar with the Vegas airspace/landmarks).

@Pondlife I believe the DC SVFR area as well as the NYC Bravo/VFR Corridor require you to have charts on board similar to LA

@Dave Thanks for the pointer! I updated my answer: NYC is another good example, but I didn't see any requirements for the DC area. Maybe it's in a NOTAM or somewhere else.

@Pondlife It looks like i was mistaken I also cant find anything that requires you to have the chart on board for the DC SFRA

@Pondlife "Near LA International..." is really just when flying the SFRA  route from Santa Monica, over LAX, and to the other side, or vice versa. ForeFlight has the info in the LA TAC Supplement, and you can zoom in on the map page to get the TAC info, so you don’t need paper charts.


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How long will one remain conscious in the event of a sudden cabin depressurization?
I know the usual scenario is where an airliner suffers from an explosive decompression and the oxygen masks drop and the plane descends to a safer altitude but.....
This is a purely hypothetical situation but if a passenger plane was cruising at 39000ft+ and it suffered a cabin leak that somehow went unnoticed by the crew and passengers and the oxygen masks didn't drop, how long roughly would it be before the passengers were incapacitated, and how long before the lack of oxygen became fatal.

The depends entirely on how fast the cabin is leaking e.g. how big the hole is.

Good question, but can we assume it takes 30 minutes to clear the cabin of something mid size like a 737, I am guessing a slow drop in pressure over that sort of time wouldn't be noticed.

Or if the cabin didn't pressurise correctly and was at outside pressure as it climbed to cruising altitude.

When an airliner suffers an explosive decompression, everybody dies of barotrauma (explosive decompression is defined as happening faster than the air can escape lungs and the pressure difference is enough to damage lungs) and the aircraft falls apart. The more normal event is a rapid decompression.

More relevant answers in Would failure to put on an oxygen mask during loss of cabin pressure result in death?

Worth mentioning is that the masks don't care how fast the pressure falls: as soon as the pressure drops below a set pressure altitude (usually 12000 feet), the masks drop.

In 747-100 and -200 aircraft, when the cabin altitude reaches 10,000 feet, an loud alarm horn goes off in the cockpit.

@JanHudec: "everybody dies of barotrauma [...] and the aircraft falls apart."  UA811, AQ243, etc., would beg to differ.

The question you're asking roughly translates to What is the time of useful consciousness at 39,000 feet?. The answer is "About 15-20 seconds, once the pressure bleeds off." The FAA has a handy table for this:

From Chapter 16 of the Pilot Handbook of Aeronautical Knowledge.
You can get a PDF of Chapter 16 here, or you can grab the whole thing from the FAA

The Time of Useful Consciousness will vary depending on personal physiological factors (e.g. if you're a smoker your blood doesn't oxygenate as well - you will probably have less time. If you're a mountain climber in excellent shape and used to breathing rarified air on your climbs you'll probably have a little more time).
In the case of a non-explosive decompression (say a pressurization system failure) you'll probably have more time than this from the start of the event to the point where everyone is unconscious: the cabin pressure will take time to bleed off. Whether that time is seconds or minutes depends on the nature of the leak.
Presumably while the pressure is bleeding off the aircraft's systems will complain about the loss of cabin pressure and give the pilots a chance to address the problem (fix the pressurization system or descend to a safe altitude). Unfortunately the effects of hypoxia can start setting in before the crew realizes what's going on (which is one of the contributing factors in the loss of Helios Flight 522, which suffered just this kind of gradual depressurization).

Thank you, that was exactly what I was looking for.  Thanks.

@Ian You may also find this article from AvWeb interesting. It discusses a lot of the other factors that I alluded to above.

Is the pressure the main factor in how long, or the fact that there is less oxygen?  I ask because I have many times emptied my lungs and sat on the bottom of a swimming pool longer than two minutes.  (I realize it is impossible to completely empty them, but I do as much as I can—otherwise, I would not be able to stay on the bottom.)

@WGroleau That is an aeromedical/physiology question above my pay grade :) I know the "time of useful consciousness" is predicated on breathing "normally" (because the decompression would burst your lungs like an uncontrolled ascent from a dive if you tried to hold your breath), and the time you have has to do with the partial pressure of oxygen in the air you're breathing after the pressure drop, but I'm afraid I don't know much more than that...

Is the loss of consciousness in this table due on rapid change in pressure? Certainly many people can remain conscious indefinitely at 20000 feet; there are even permanent settlements as high as 17000. Or are the figures just aimed at average or worst-case health conditions?

@R.. These are average figures for low-landers (folks living from sea level to say 3000 feet), but in general there are very few people who can remain usefully conscious indefinitely at 20,000 feet. This is an important distinction: You may still be awake and think you're fine, but you're actually a babbling idiot (altitude chamber videos are always good for a chuckle). Someone from La Rinconada, Peru (elevation of almost 17,000 feet) would probably last longer than 30 minutes, but that's a minuscule slice of the population.

authors: שלמה ויינשטיין


text:
Why do I have to turn off my (non-cellular) iPad before takeoff?
Every time I travel on an airplane, the stewardess forces me to shut down my iPad.
I just lock it, and start using it again 5 minutes later.
I wonder why this is? Is it because I have to have my hands free if the airplane crashes? Or is there any other logical explanation?

They still require you to shut it down, not lock it, so the question title is a bit misleading. They're also asking you to switch off electronic devices; so I'd assume it has something to do with electricity or electromagnetics.. :) I've often heard the hands-free argument, but that doesn't hold up, as it's perfectly fine to sit and flip through the Gutenberg Bible or other heavy-weight book of your choice.

Hopefully your question will eventually be obsolete (not holding my breath though): http://www.faa.gov/news/press_releases/news_story.cfm?newsId=15254

possible duplicate of Why aren't cell phones allowed to be used in aircraft?

A pilot told me that for the most part unless the laptop or pad was sitting right next to the instrument panel it would no cause any trouble. It would have to be directly in the cockpit about an inch away from the instrument. Would you really fly on a plane that if one cellular phone sitting in the back could cause you to crash would you really go. No, probably not.

@DannyBeckett not really a duplicate, that question is about the radio transmitter in the phone, not the rest of the device (i.e. in flight mode). This one is about turning off electronic devices during takeoff and landing. Also electromagnetic radiation is still radiation (and can cause radio interference), not all radiation is from radioactivity ;)

Since the rules are different in different countries, this would very much depend on where you are asking about.  Please update your question to include that information or the rules that you are asking about (faa, easa, etc.)

@roe anything with an antenna is emitting, and an iPad has an antenna. At the very least it had WiFi and GPS, many have 3G (thus a cellphone functionality just like that phone).

@jwenting; anything doing electricity with any kind of frequency is emitting, you don't need an antenna for that. The point is if you're not actually trying to transmit anything, such as when your device is in flight mode, the radiated effect will be comparatively low, and from how the question was asked, I assumed the iPad would be in flight mode.

@roe I know that, which is one reason to ban ALL electrical devices during start and landing.

@yankeekilo, By the time this question was asked, it was already obsolete in the U.S. Delta and JetBlue had their plans compliant with the FAA reg change that you linked within a couple of days of that press release and were already allowing passengers to use non-cellular electronic devices during all flight phases last November. The only exception is that devices above 2 lb must be stowed beneath the seat or in the overhead during takeoff and landing so that they don't become projectiles.

Actually, they don't!  Well, not always anyway.
The FAA recently issued a press release titled FAA to Allow Airlines to Expand Use of Personal Electronics.  This press release allows for the use of some electronics, including iPads and similar devices, during all phases of flight,.  However, it is up to each airline to change their procedures and to determine which devices can be safely used.
This is a small excerpt from the press release:

Passengers will eventually be able to read e-books, play games, and
  watch videos on their devices during all phases of flight, with very
  limited exceptions. Electronic items, books and magazines, must be
  held or put in the seat back pocket during the actual takeoff and
  landing roll. Cell phones should be in airplane mode or with cellular
  service disabled – i.e., no signal bars displayed—and cannot be used
  for voice communications based on FCC regulations that prohibit any
  airborne calls using cell phones.    If your air carrier provides
  Wi-Fi service during flight, you may use those services.  You can also
  continue to use short-range Bluetooth accessories, like wireless
  keyboards.

I flew on Jet Blue the day after that press release and they were already allowing iPads and similar devices as long as they were in airplane mode.  Other airlines will follow soon I'm sure, but their manuals and procedures must be updated and approved by the FAA first.

Originally the regulations were introduced because electronic devices ALL transmit, especially those with antennas (and an iPad has 2-3 of those built in).
That forcing people to turn them off helps keep attention at the safety briefings helps a lot. Rather than having several hundred passengers playing minecraft, reading papers, watching videos, they now have less on their mind and might actually watch that safety briefing for a change.

And of course rather than argue with every passenger who claims "but my device doesn't emit anything" and having to have 10.000 page lists of what's allowed and what isn't by product numbers, far easier to just exclude everything.

But having several hundred people playing sudoku, reading papers, and flipping through comic books is just fine? I don't buy it (not questioning the emission part), I don't think the platform you use to entertain your mind play a vital factor in how much you pay attention to the safety briefing.

@roe and if you do that during the safety briefing you get asked to put it aside as well...

interesting, never experienced that. I usually at least pretend to pay attention out of professional courtesy, but there are plenty of opportunities to ask people around me to put their stuff aside.

The only time I've ever seen flight crew ask pax to pay attention was when pax were in the emergency exit seating, and even then I haven't seen it much at all. I'm not the world's most frequent commercial flier, but I get in around 40 flight segments a year.

@jwenting and if you had an iPad you could be asked to set it down. I don't see the difference...

@flyingfisch which is exactly my point... The rules are made universal for ALL electronic gadgets so they won't get into endless arguments "but mine doesn't do anything", and to be able to get people "I'm just listening to some music" to set their device aside.

@jwenting "and if you do that during the safety briefing you get asked to put it aside as well..." By whom, exactly? The cabin crew are busy giving the safety demonstration and who else is there?

@DavidRicherby they do a walk through the cabin right before the briefing... And ever more they're not that busy during the briefing as it's now mostly handled by video screens rather than the cabin crew.


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Does the profit from selling duty-free items on board justify flying the carts?
Some airlines have duty-free carts (2) with items for sale on board. It seems that only a few items get sold each flight. Does the profit from selling a few items justify the cost of having this extra weight/volume on board?

This is more of an airline-to-airline based question, which might bring-in some opinionated answers. Needless to say, the total weight of the duty-free items would be negligible when compared to other weight on the aircraft.

In this answer I calculated the cost of taking a few extra kgs on a Airbus A380 http://physics.stackexchange.com/a/133893/52188

@ROIMaison, so with 0.61 liter per kg, assuming 2 carts+items weigh 100kg, it's 61 liters (~$200). This means the average profit from all sales must exceeds ~$200.

Seems like a lot. Probably airlines pay less for fuel?

"average profit from all sales must exceed ~$200", we are now in the opinion domain... who knows if sales from the cart must be profitable? Maybe there are other indirect benefits from selling these items.

It clearly is a benefit since it exists.  Airlines would not carry additional weight with no benefit.

^^^ I dunno, they carried flight engineers for several decades. :-)

Related: Delta ceases duty free sales today

@ROIMaison I've made similar calculations for an A330-300 over at Travel.SE.

Do they bring a cart on board that they use only for the duty-free stuff, or do they unload the leftovers from another cart and load the duty-free stuff on it in flight? In the latter case the fuel cost is only the cost to fly the actual items for sale, and if there are very few sales then they only need to stock the cart with a few items, so the added weight may not be much at all. But none of my international flights have ever had such a cart, so I have never had a chance to observe how they are prepared.

@DavidK I've seen both. Having dedicated carts for everything makes loading and offloading faster of course, having fewer carts that are loaded during the flight saves a bit of weight (but requires dedicated storage lockers for all the items, adding weight).

Okay so there are a few points to this

Lots of different things are sold - perfumes etc, gifts, "in flight" convenience items such as headphones, plus food/drink. That means lots of sales opportunities.
"Luxury" items are high margin anyway: perfume is a big profit item even with duty. By knocking the duty off and making it "feel" cheap: they can potentially sell it for more than the RRP (minus duty), and thus make more profit than a regular shop, despite selling it for less (gross) to the passenger
You only need to carry one or two bottles of each perfume, as you won't sell a ton of them. They don't take up much space: perfumes etc are only sold to one or two people per flight, they're not the reason the cart is there... they're just an extra. Similarly headphones: you won't sell many, but you'll definitely sell some when somebody realises they left theirs at home: I bought a set of cheapo £2 headphones for £8 at a train station a few days ago because wasting £6 on a set of crappy headphones was better than the idea of a 5 hour train without any music. People will pay for convenience, and carrying one or two of these items doesn't take up much space at all.
Food/drink are the reason the cart is there. When on a flight for 1-4 hours, some people are going to be hungry/thirsty... and you have anywhere from 100 to 850 passengers. The markup on these items can be huge - £6 for a small can of beer, for example, which would cost <£0.30 from a wholesaler. You don't need to sell a huge number of pies/burgers/cans of beer/£3 cans of coke to make a decent profit. With the air-con on a plane, I find I get very thirsty and will go through a 500ml drink roughly once an hour. Similarly on a 4+ hour flight I'll tend to want a snack or meal at some stage. I'm certainly not alone in this.
Seats on these planes aren't always that expensive. On my last flight it was less than £40 for my one-way ticket on a 2 hour flight: if the trolley takes up roughly one seat's worth of space, they only need £40 in profit (or perhaps 20 cans of coke in 2 hours, at £2.50 per can) to be worth carrying a trolley. Similarly the longer the flight, the more likely people are going to be thirsty. With 190 people on board, even if only one in 10 buys a drink, that trolley has made more profit than my seat. Even considering an 8 hour transatlantic flight with 400 people on board a 767, that still only needs half the flight to buy one drink (which they probably will in 8 hours...) to make up for my £500 seat
It's expected, and is a service to some extent... people would start getting quite annoyed if they found they couldn't get a drink on the flight, even if said drink is expensive. People tend to expect to be able to get a drink, if nothing else, but usually food too. Notice that most non-local (2hr+) trains (and many local ones!) tend to have a trolley service or, more and more often, a shop on board? Even if it didn't make a profit at all, it may be worthwhile for customer happiness. This is a bit of a moot point, though, as trolley services are definitely profitable (trust me, if it wasn't, Ryanair wouldn't provide one)
Your cabin crew are there anyway for safety reasons, why not put them to use as sales people? Otherwise they're just sitting relatively idle for much of the flight. Not that I wish to discredit the work and important role that cabin crew play: they're far more important than most of us realise... but the fact remains that for much of the middle of the flight, on a routine flight and unless something goes wrong, they don't actually necessarily have that much to do considering the number carried.
The cart may be there anyway! On longer flights with meal services, the airline will already have the cart available for set times. Why not put a few bottles of perfume in the bottom for an extra profit?
Capacity limits. Aircraft aren't always limited purely by space or weight: they're also only certified to carry a set number of passengers due to things like the number of emergency exits. It may be that you can't actually carry more passengers even if you want to
The trolley can fit into space a person wouldn't. A trolley isn't person shaped, and can be stored somewhere near the back of the plane (eg where the fuselage tapers) that you couldn't fit another seat even if you wanted to. Why not use the space for something useful?

For an airline there may be other benefits beyond direct financial profit from the sales.
It's a bit of customer service, allowing passengers to buy things on board they may have forgotten to pack for example.
And a lot of the items they have are branded, which adds marketing value as the items are often purchased as gifts for friends, family, and business associates by people who didn't have opportunity to do so before the flight.

TBH because of the often inflated prices and (to me) unappealing selection of items I rarely buy anything unless the carrier accepts cash in some currency I have left over that's impossible to exchange back home.


text:
How much does go-around cost?
What is the extra cost of aborted landing and go-around for typical "big" airliner?

not that much compared to the entire flight, at most it's some extra fuel and delay

There is when you're doing your twin rating on a budget!

Much less than landing that should have been a go-around.

A lot of aircraft arriving at busy airports spend an indeterminate amount of time circling in a holding stack anyway. The cost of a go-around must be negligible by comparison with overall flight costs.

I don't understand the question. It directly cost fuel and flight time, but it cannot be compared to what happen if the aircraft land. If the pilot decide to go around, it is becaus landing the aircraft could cost life (not enough visibility, collision with other vehicle,...) and thus go around save money and lives. You cannot say it costs something.

@ManuH a go-around can also be done as an exercise when you are training. In this case, nothing special happens if the aircraft lands instead of doing a go-around. So you can say it costs something.

@ManuH: The fact that another option costs more or has other consequences shouldn't prevent to evaluate the cost of  go-around (which must be taken into account when pricing the ticket anyway).

Same as "how much the maintenance costs", this question has nothing to do with consideration that not worth doing because expensive.

@mins Are you saying pricing must take into account the probability of a go-around (e.g. be cheaper if weather at arrival is good)?

@ManuH: I'm just saying that all operational costs must be taken into the pricing process, including actual go-around in the past. Not less, not more than the quantity of coffee actually used, or the actual number of tires used in the past. When the price is issued, the company must know the profitability, thus the costs of everything. If winds increase due to global climate change, triggering more go-around, then the price will indeed increase.

We can look at financial data from airlines to estimate these figures.
In addition to fuel, there will also the extra duty time for the crew, some delay in schedule, and extra flight time on the aircraft. The delay in schedule can be difficult to estimate, but other costs of operation can be estimated. A short flight would take 1.5 hours, and the go around might take 0.2 hours.
Based on the financial data, an MD-83 might cost about 6000 dollars/hour to operate. This includes all direct operating expenses. This means that the regular flight would cost about 9000 dollars to operate, and a go around would cost about 1200 dollars. Since a go around uses a lot of fuel, the figure may be a bit higher.
The figures for a Boeing 747-400 show about 15000 dollars/hour to operate, and a Boeing 777-200 about 12000 dollars/hour to operate. That would make an 8 hour flight 120,000 dollars and 96,000 dollars respectively, with go arounds costing 3000 and 2400 dollars respectively. Obviously, for longer flights, the go around will cost less proportionally than for a shorter flight.
As DeltaLima mentioned, the cost of not doing a go around (which includes making this decision early enough) can be substantially higher. Loss of or even just damage to an aircraft will cost much more time and money.
To see if these numbers make sense, this report mentions that an empty MD-83 would need 1000 kg of fuel for a go around and new approach. It also mentions that a ferry flight from Paris Orly to Olbia, Italy, would normally require 6800 kg including reserves. If reserves are about 1600 kg, this would mean that the flight would use 5200 kg of fuel.
If jet fuel costs 3 dollars per gallon, this comes out to 985.72 dollars of fuel for a go around, and 5125.73 dollars of fuel for a regular flight. This figure seems reasonable along with the figures above.

Is there any extra cost of ground handling if plane arrives late or couldn't depart in time?

This "$6000" per hour approach is somewhat flawed because not all expenses directly and proportionally depend on the duration of flight. I suspect, longer flight should be cheaper per hour.

@AudriusMeškauskas you are correct, using the average cost per hour will result in some error, but it does give a rough idea. I'm not sure what the best way is to get a closer estimate.

@h22 While it certainly won't be exact, not all of the costs would actually be less per hour. The cost of paying the crew will be the same per hour and the fuel cost will actually be more per hour (because of the TOGA power climb out and lots of extra flying around at inefficient altitudes.) I wouldn't be surprised if the higher per-hour fuel burn mostly made up for the lower per-hour costs in other areas (i.e. per-flight costs and the like.)